1. Field of the Invention
This invention relates to rocket nozzles, especially to those that are extendible, and to means for deploying extendible exit cones of such nozzles.
2. Description of the Prior Art
A conventional thrust nozzle exit cone for rocket motor ballistic missile systems is designed for optimum performance at the median altitude of the intended trajectory. One of the functions of the exit cone of a rocket nozzle is to provide an inclined surface against which the expanding exhaust plume of the rocket can bear, and thereby to provide some of the forward thrust of the rocket. The exhaust plume grows larger with increasing altitude of the rocket, because of the decreasing pressure of the ambient atmosphere. Hence, in a conventional rocket nozzle, the exhaust plume is initially too small for the available surface area of the exit cone. This permits formation of a partial vacuum inside the edges of the exit cone, which creates an atmospheric drag on the rocket. At high altitudes, the exhaust plume is too large for the exit cone, so that much of its potential energy is unused.
A rocket nozzle that is sufficiently large to make full use of the expanding exhaust gases of a rocket in the low ambient pressures at high altitudes would normally occupy an inordinate proportion of the available storage space in silos, submarines, aircraft, or between stages of a multistage missile. Hence, there is a need in rocket motor ballistic missile systems for such a rocket nozzle that can be made to fit into a minimal storage space.
Various solutions have been proposed for this problem. These have included the use of inflatable exit cones, exit cones that are flexible and can be folded in various ways, exit cones formed by overlapping segments similar to the petals of a flower, and exit cones segmented longitudinally, as in the present invention. However, each of these ideas has produced its own problems, so that none has been entirely successful.
The present invention is essentially an improvement on an invention by the same inventor, described in a paper titled "Nested Extendible Exit Cone Solid Rocket Nozzle Engineering Evaluation Program," published in July of 1978, hereinafter termed "the prior invention." That paper described a rocket nozzle exit cone made to be extendible by a plurality of longitudinally divided segments. The first segment had the form of a conventional, convergent-divergent thrust nozzle attachable to a rocket case. The other segments were successively larger, conic annuli, movable relative to the first segment. In their stowed position, these movable segments surrounded the first segment. They were deployed into their extended positions by moving them aftwardly along the axis of the nozzle until they formed a single exit cone with that of the first segment.
The means in the prior invention for deploying the movable segments comprised a plurality of long screws that joined adjacent nozzle segments together. Each screw of a set passed through a threaded lug on the upstream segment of an adjacent pair and its aft end portion was seated in a socket fixed to the downstream segment so that rotational motion of the screw was permitted. All of these screws were synchronously rotated by a system of gear boxes and flexible shafts that were, in turn, rotated by a gas-actuated turbine, powered by compressed helium. A primary flexible shaft attached to gears rotated by the turbine joined the flexible shaft train of each set of screws.
The source of gas in this system was a pressure vessel filled with liquid helium under high pressure. The pressure vessel was opened to the system at the desired time by an explosive device that ruptured a diaphragm in the pressure vessel. The explosive device, in turn, was operated, via an electrical system, by a signal produced either by a timer or from ground control.
In operation, the screws were rotated very rapidly by the gas operated turbine and the movable nozzle segments were joined together into their deployed positions with considerable force. The shock of deployment was absorbed somewhat by an elastomeric ring seated between each pair of adjacent conic segments. This ring also functioned as a hot gas seal. A plurality of plug-and-receptacle latching mechanisms locked each pair of adjacent segments into its fully deployed position.